looks like a deficiency. . . maybe iron? I am not that great w/trees - is this only a part of the tree - a branch? Otherwise, it's not a very large tree! lol

No clue on the species . . .

I would use chelated iron mixed with water. Water the tree well, pour on the c. iron mix, water in well. Should help with the yellow leaves. I'm not sure of the ID but it's on the tip of my pea brain....some kinda tropical methinks, can't pull the name from the rolodex in my head....but it's right there. Someone else, probably younger than me, will be along!!

It looks like it might be a Tipu tree.

Certain trees will shed their leaves in the spring so that the new growth will have more water and nutrients. The Live Oaks in my area are shedding leaves right now in order to put out new growth.

An alternative treatment would be to dig in a whole lot of elemental sulfur around the tree at the drip line. Definitely use the iron first as the immediate remedy but use sulfur for the long run.

I agree it looks like Tipu (Tipuana tipu), a South American native. First, make sure it's getting the correct amount of water at the correct interval. For example, a tree with a canopy 15 feet wide will need about 130 gallons of water each time you apply. This time of year in the Phoenix area Tipu trees should be watered once every 2 - 4 weeks, depending on the weather. By late May and through summer water once every 1 - 3 weeks. Details on watering can be found in Landscape Watering by the Numbers. Page 9 has a table for the amounts and page 18 will show you how often.

Trees often have yellowing leaves right before the new growth season. They shed the prior year's leaves and replace them with new ones. As long as you are watering correctly, I don't think your trees yellow leaves/leaflets are anything to worry about.

Also, Tipu trees are a member of the pea or legume family. They are unique in the fact that they can 'make' their own nitrogen through a symbiotic relationship with a bacteria in the soil. No additional nitrogen is needed for plants in this group which also includes palo verde, mesquite, ironwood, acacia, etc.